Liquid separators of the known type are provided with a centrifugal separator and a fine separator with a flow-through element through which a gas to be purified can flow, whereby the centrifugal separator consists of a cylindrical housing having a tangential inlet and an axial outlet, which housing defines an inner space in which has either or not been provided a screen to guide the flow towards the outlet.
In the known liquid separator, the above-mentioned fine separator is entirely formed of the flow-through element, and this flow-through element, for example in the form of a coalescence filter, is provided in the inner space of the cylindrical housing of the centrifugal separator, and the flow-through element is erected such that, if the above-mentioned screen is present, said screen extends around the flow-through element, to which end the screen has been made in the shape of a cylindrical tube.
When using a known liquid separator, a mixture of gas and liquid is supplied via the above-mentioned tangential inlet, for example in the form of compressed air coming from an oil-injected compressor.
As the above-mentioned inlet is placed tangentially on the cylindrical housing, the incoming mixture of gas and liquid, as is known, is subjected to a whirling motion, whereby a pre-separation occurs since, due to the centrifugal effect, the relatively heavy liquid particles are swung against the inner side of the cylindrical wall and carried off along said wall to the bottom of the liquid separator due to the gravitational force, where the separated liquid can be discharged if required, for example via a liquid outlet provided to that end.
The gas from which the relatively heavy liquid particles have been separated subsequently flows, as is known, via the space between the screen and the flow-through element if a screen is present, or via the space between the housing of the centrifugal separator and the flow-through element, through the flow-through element in order to separate the smaller liquid particles which are still present in the gas flow.
Finally, the purified gas flow leaves the liquid separator via the gas outlet, so as to be subsequently used for example for further applications.
A disadvantage of the known liquid separators is that, because of the presence of the above-mentioned flow-through element in the housing of the centrifugal separator, they are relatively sizeable and expensive.
Another disadvantage of the known liquid separators is that, because of their relatively large dimensions, they come under a stringent inspection category, which is disadvantageous as far as the cost of the inspection is concerned.
When such known liquid separators are applied to the compressed air line of an oil-injected compressor, as the compressor switches from a loaded to an unloaded condition, the gas volume is blown off as a whole from the space in the housing of the centrifugal separator through the fine separator until the equilibrium pressure for the unloaded working condition is reached.
The relatively large air volume has to be blown off quickly so as not to restrict the number of loaded/unloaded cycles too much.
A disadvantage thereof is that, as the blowing off is done quickly, the oil will strongly foam. The rising foam and the contamination that is solved therein deteriorate the operation of the fine separator, result in an excessive oil consumption and also reduce the life of the fine separator.
An additional disadvantage of the known oil separators is that the flow-through element, as a result of the pressure relief and the accompanying high gas velocities, is mechanically loaded while a volume of gas is being blown off during the transition from a loaded to an unloaded condition of the compressor, which is disadvantageous to the life span of said flow-through element.